This invention relates to a detector device for measuring the intensity of electromagnetic radiation.
It is known to use an imaging charge-coupled device (CCD) to generate an electrical signal representative of the distribution of light intensity in the image plane of a lens. One form of imaging CCD comprises a silicon die which has been processed using conventional MOS technology to form a plurality of buried channels beneath its front surface (the surface through which the die is processed). Each channel is made up of a linear array of like elementary regions. A clocking electrode structure overlies the front surface of the die, and by application of selected potentials to the clocking electrode structure, charge present in a given elementary region of a channel may be advanced through the linear array of elementary regions, in the manner of a shift register, and extracted from the channel. In an imaging CCD, charges are generated in the channels photoelectrically. Thus, if a photon enters the die, it may cause generation of conduction electrons and these conduction electrons may enter a channel layer and become confined in one of the elementary channel regions.
The imaging CCD is placed with one of its surfaces at the focal plane of a camera so that the camera lens forms an image of a scene on that surface. The CCD may comprise, e.g., 64 parallel channels each having 64 elementary regions and the resulting 64 .times. 64 array of elementary regions resolves the image receiving surface of the die into 64 .times. 64 picture elements or pixels. The camera has a shutter which is opened for a predetermined exposure interval, during which all electrodes of the clocking electrode structure remain at constant potentials. The shutter is then closed, and the charge accumulated in the elementary channel regions is clocked out of the CCD. The intensity of the optical energy incident on a given pixel during the exposure interval can influence the electron population of the associated elementary region of the channel layer, and so the number of electrons that are transferred out of the elementary region, and ultimately extracted from the CCD, is representative of the intensity of the light incident on the pixel. In this manner, the CCD can be used to generate a two-dimensionally sampled electrical signal representative of the distribution of light intensity over the image receiving surface of the CCD, i.e., of the image formed by the camera lens.
An imaging CCD of the type that has previously been described is useful for providing a signal that represents an arbitrary image. However, such an imaging CCD is complex in its structure and is difficult to fabricate.
When a Fabry-Perot etalon is illuminated using collimated monochromatic light and the transmitted beams are brought to a focus, a pattern of interference fringes is observed in the focal plane. The fringes are circular and concentric and the spacing between the fringes is a function of the wavelength of the illuminating light and the separation of the etalon plates. Accordingly, the image produced from such a light source using a Fabry-Perot etalon is not arbitrary.
In a conventional CCD, in which adjacent clocking gate electrodes are electrically isolated from each other, potential barriers may exist between adjacent clocking gate electrodes, and these barriers may interfere with transfer of charge through the device under control of the clocking gate electrodes. U.S. Pat. No. 3,728,590 issued Apr. 17, 1973 (Kim et al) discloses a CCD in which resistive material is provided between, and is electrically connected to, adjacent clocking gate electrodes. Use of the resistive material eliminates potential barriers between the clocking gate electrodes. H. Heyns and J. G. Van Santen, The Resistive Gate CTD Area-Image Sensor, IEEE Trans. Electron. Devices, ED-25, 135-139, Feb. 1978, describes use of a resistive gate to control transfer of charge in an imaging CCD. J. A. Higgins, R. A. Milano, E. A. Sovero and R. Sahai, Resistive Gate GaAs Charge Coupled Devices, GaAs IC Symposium, IEEE, 49-52 (1982), describes a resistive gate CCD fabricated using GaAs.